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Facile Photochemical Syntheses of Conjoined Nanotwin Gold-Silver Particles within a Biologically-Benign Chitosan Polymer

1
Department of Chemistry, University of North Texas, Denton, TX 76203, USA
2
Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA
*
Authors to whom correspondence should be addressed.
Nanomaterials 2019, 9(4), 596; https://doi.org/10.3390/nano9040596
Received: 6 March 2019 / Revised: 1 April 2019 / Accepted: 4 April 2019 / Published: 11 April 2019
(This article belongs to the Special Issue Plasmonic Nanostructures and Related Applications)
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Abstract

A simple photochemical method for making conjoined bi-metallic gold-silver (Au/Ag) nanotwins, a new breed of nanoparticles (NPs), is developed. To the best of our knowledge, the photochemical method resulted in distinct, conjoined, bimetallic nanotwins that are different from any well-established alloyed or core-shell nanostructures in the literature. The conjoined Au-Ag NPs possessed surface plasmon resonance (SPR) properties of both metals. The bimetallic nanostructures possessing distinctive optical properties of both metals were obtained using Au NPs as seeds in the first step, followed by the addition of a silver precursor as feed in the second step during a photochemical irradiation process. In the first step, small, isotropic or large, anisotropic Au NPs are generated by photoinduced reduction within a biocompatible chitosan (CS) polymer. In the second step, a silver precursor (AgNO3) is added as the feed to the AuNPs seed, followed by irradiation of the solution in the ice-bath. The entire photochemical irradiation process resulting in the formation of bimetallic Au-AgNPs did not involve any other reducing agents or stabilizing agents other than the CS polymer stabilizer. The small, conjoined Au-Ag bi-metallic NPs exhibited SPR with peak maxima centering at ~400 nm and ~550 nm, whereas the large conjoined nanoparticles exhibited SPR with peak maxima centering at ~400 nm, 550 nm, and 680 nm, characteristic of both gold and silver surface plasmons in solution. The tunability in the SPR and size of the bimetallic NPs were obtained by varying the reaction time and other reaction parameters, resulting in average sizes between 30 and 100 nm. The SPR, size, distribution, and elemental composition of the bi-metallic NPs were characterized using UV-Vis absorption, electron microscopy, and energy dispersive X-ray spectroscopy (EDS) studies. View Full-Text
Keywords: isotropic; anisotropic; photochemical; bifunctional; nanomaterials; plasmonic isotropic; anisotropic; photochemical; bifunctional; nanomaterials; plasmonic
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Korir, D.K.; Gwalani, B.; Joseph, A.; Kamras, B.; Arvapally, R.K.; Omary, M.A.; Marpu, S.B. Facile Photochemical Syntheses of Conjoined Nanotwin Gold-Silver Particles within a Biologically-Benign Chitosan Polymer. Nanomaterials 2019, 9, 596.

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